In the fabrication of laminated safety glass, it is customary to place a piece of thermoplastic sheeting between two pieces of float glass. It is also common that the thermoplastic interlayer""s surface can be roughened to avoid blocking, i.e., one layer of interlayer sticking to another. The roughness on the interlayer can also allow the interlayer to be moved while the two pieces of glass are aligned as the glass/interlayer/glass sandwich (hereinafter, xe2x80x9cassemblyxe2x80x9d) is constructed. In constructing such an assembly, air is trapped in the interstitial space between the glass surface and the bulk of the thermoplastic interlayer. Trapped air can be removed either by vacuum de-airing or by nipping the assembly between a pair of rollers.
In the case of vacuum de-airing, air is removed while the assembly is at ambient temperature. Tacking of the interlayer to the glass and sealing of the edges is accomplished by heating the entire assembly while it is still under vacuum. The assembly, after the heating step, is generally referred to as a pre-press or a pre-laminate.
In the case of nipping, the assembly is generally heated to a temperature between 50-100xc2x0 C., and is then passed through one or more sets of nip rolls. Edge sealing is accomplished by the force of the rollers exerted on the two pieces of glass. At the end of the nipping step, the assembly is called a pre-press. In windshield manufacture, the nip rolls are often articulated so as to accommodate the curvature in the windshield. When complex shapes and angles are involved, or when several models of windshields are made concurrently, it is often more convenient to use the vacuum de-airing method.
However, laminators may encounter a dilemma when selecting a suitable interlayer. It is sometimes difficult to choose an interlayer with optimal features for pre-pressing, namely, rapid air removal and proper edge seal. Interlayers which have rougher surfaces as measured by the 10-point roughness (ISO R468), Rz, can allow for faster de-airing. However, such interlayers can make it inconvenient to obtain edge seal as more energy is generally required to compact the rough interlayer. If the edges of the pre-press are not completely sealed, air can penetrate the edge in the autoclaving step where the pre-press is heated under high pressure, and can cause visual defects in the laminate which is commercially unacceptable. Laminators who use vacuum for de-airing in hot environments can have added difficulty. Interlayers that are rough and allow for rapid de-airing at about room temperature (23xc2x0 C.) often do not de-air as well when the ambient temperature is much above 30xc2x0 C.
On the other hand, relatively smooth interlayers can lead to the edges sealing before sufficient air is removed, and can leave air trapped inside the pre-press. This problem is commonly referred to as pre-mature edge seal, and can be especially common with PVB interlayers. During autoclaving, the excess air may be forced into solution under high pressure, but may return to the gas phase after autoclaving. Defects which occur after lamination are often more costly to rectify.
The thermoplastic interlayers of this invention allow for rapid de-airing even at high temperatures, and also allow good edge seal to be obtained.
In one aspect the present invention is a glass/adhesive sheet laminate comprising at least one layer of glass and a sheet of plastic interlayer, said plastic interlayer having at least one surface embossed with a pattern which provides relatively uninterrupted channels for de-airing in two intersecting directions, said channels having depth between 20 microns and 80 microns, and width 30 microns to 300 microns and spaced between 0.1 mm and 1 mm apart.